Process chamber cooling

ABSTRACT

A method is provided for the rapid cooling of a processed semiconductor wafer after a wafer heating by radiation process. The method includes the introduction of a radiation absorbing material element between the processed wafer and highly reflective surfaces—after a wafer heating by radiation process. The highly reflective surfaces reflect and re-direct radiant energy from the processed wafer and its surrounding components back to the processed wafer, impeding its cooling process. The radiation-absorbing material element, once between the processed wafer and the highly reflective surfaces, absorbs radiation from the processed wafer and its surrounding components, expediting their cooling process. Accordingly, significant time is saved for the cooling process, thus improving overall wafer throughput.

REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of application Ser. No.09/454,377, filed Dec. 3, 1999, which is owned by the assignee ofrecord, ASM America, Inc.

FIELD OF THE INVENTION

[0002] This invention relates generally to equipment for processingsemiconductors, and more particularly to methods and apparatus forrapidly cooling substrates.

BACKGROUND OF THE INVENTION

[0003] There are numerous semiconductor process steps involved in thedevelopment of modem day integrated circuits (ICs). From the initialfabrication of silicon substrates to final packaging and testing,integrated circuit manufacturing involves many fabrication steps,including photolithography, doping, etching and thin film deposition.For many of these processes, temperature is a key factor for obtainingdesired film properties and characteristics. Characteristics of thinfilm metals and dielectrics affect electronic properties such asresistive and capacitive values, thus directly affecting IC performancecharacteristics such as device speed and power consumption.

[0004] In most semiconductor processes, heating by radiation is thepreferred mode for heating because of its rapid heating capabilitycompared to heating by conduction and convection. In a system wheresingle wafers, or wafer batches are being processed, wafer throughputwould be directly affected by the rate at which each wafer or each batchof wafers are heated and subsequently cooled. In such systems whereheating by radiation is employed, a rapid cooling method shouldcompensate to otherwise not compromise the high wafer throughputachieved by the rapid heating by radiation process.

SUMMARY OF THE INVENTION

[0005] These and other needs are satisfied by several aspects of thepresent invention.

[0006] In accordance with one aspect of the invention, a workpiece isplaced on a support or susceptor within a process chamber, and processedto an elevated temperature. A radiation-absorbing medium or materialelement is positioned between a reflective surface and the workpieceafter a semiconductor process. The material element is spaced from theworkpiece more than about 5 mm. The medium allows for the processedworkpiece to cool from the elevated temperature.

[0007] In accordance with another aspect of the invention, a method isprovided for processing a substrate in a semiconductor-processingchamber. A semiconductor substrate is placed on a substrate supportwithin the processing chamber. A radiation-absorbing material element ispositioned between a reflective surface and the substrate after heatingof the wafer, outside the processing chamber.

[0008] In accordance with another aspect of the invention, a hightemperature processing apparatus is provided, including a processingchamber and support the chamber for supporting a substrate. A pluralityof heat sources are positioned outside the processing chamber to provideradiant energy to the substrate. A highly reflective surface placedoutside the heat sources promotes an efficient conveyance of radiatedenergy to the substrate. A movable radiation-absorbing material elementis included. The apparatus is configured to move the movable elementfrom a process position that does not interfere with heating thesubstrate during a fabrication process to a post-process positionbetween the reflective surface and the substrate after the fabricationprocess.

[0009] Advantageously, the preferred method provides significant timesavings over previous methods by expediting the cooling process of awafer after a semiconductor process is completed. The introduction of aradiation-absorbing material element between the reflective surfaces andthe wafer inhibits radiation from returning to the wafer, which wouldgenerally slow the cooling rate of the processed wafer. Conversely,rapid cooling of processed wafers thus improves overall waferthroughput.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Further objects and advantages of the invention will becomeapparent from a consideration of the drawings and ensuing description inwhich:

[0011]FIG. 1 is a schematic view of a process chamber during a hightemperature process, wherein a workpiece is being heated;

[0012]FIG. 2 is a schematic view of the process chamber of FIG. 1 aftera semiconductor process, illustrating re-radiation and reflection ofenergy;

[0013]FIG. 3 is a schematic view of a process chamber constructed inaccordance with a preferred embodiment, including a radiation absorptionmedium;

[0014]FIG. 4 is a schematic view of a process chamber constructed inaccordance with another embodiment of the invention, having a sheet ofwater formed in a double-wall quartz chamber;

[0015]FIG. 5 is a schematic top view of a double-wall quartz chamber,illustrating the laminar flow of water in a sheet-like formation withinthe double-wall;

[0016]FIG. 6 is a flow chart generally showing steps for cooling wafersin accordance with the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] As noted above, a large number of fabrication processes ofsemiconductor devices and components involve heating and cooling.Productivity or throughput is sometimes dependent upon how fast aprocess or a system heats or cools.

[0018] In many processes, such as rapid thermal processes (RTP),radiation is the primary means of heating substrates. The systems aredesigned such that the majority of radiation is contained within thesystem by multiple reflection to facilitate the heating. With thepresence of highly reflective coatings in the process system, energyfrom the radiant heat sources will be reflected and efficientlyre-directed towards the wafer.

[0019] Similarly, as substrates are being processed, or thereafter,radiation from the heated substrate would also irradiate energy andwould as a consequence reflect against the highly reflective coatings.During a semiconductor heating process, reflection of radiation from theheated substrate would further enhance the heating rate of the substratebeing processed.

[0020] Conversely, however, containing radiation within the system bymultiple reflection significantly impedes the cooling process. Manyprocesses prefer cooling of the heated substrate by turning off orattenuating the energy from the radiant heat sources and by notintroducing a separate cooling agent. Reflection of the radiated energyemitted by the heated substrate would thus impede the cooling of theheated substrate. The result is a slow cooling which directly limits thefabrication productivity or throughput.

[0021] In general, heat transfer processes occur by three basicmechanisms or modes—conduction, convection and radiation. Heat transferby radiation (q_(r)), which can be either heat emitting or absorbing, isexpressed by the equation q_(r)=σAεT⁴ where a is the Stefan-Boltzmannconstant, A the surface area of the heat transfer body, E theemissivity, and T the absolute temperature of the heat transfer body.Therefore, heat transfer by radiation can be more significant at hightemperature ranges than heat transfer by conduction or convection—bothof which are proportional only to the first power of the temperature.This equation also indicates that heat transfer by radiation can beenhanced by increasing the surface area and by using high emissivitymaterial. In addition, heat transfer by radiation is in the form ofelectromagnetic waves, which unlike conduction and convection, does notinvolve a material medium through which energy travels. Therefore,radiation can be transmitted, reflected and absorbed.

[0022] A typical process module comprises elements such as heat sources,process chambers, susceptors, ring assemblies, highly reflectivecoatings and wafers. Most semiconductor processes involve heating of asemiconductor substrate or wafer to a desired elevated temperature. As aresult, process modules are designed to efficiently convey energy from aheat source to the wafer plane by placing a heat source directly above,and sometimes below the wafer. Typically, wafers are placed on a wafersupport or susceptor within a process chamber. The chamber houses thesusceptor and ring-assembly, and allows for a robot arm to insert andretrieve semiconductor wafers for processing.

[0023] Preferred Process Chamber

[0024]FIG. 1 shows a process module 10, including a quartz processchamber 30, constructed in accordance with a preferred embodiment, andfor which the methods disclosed herein have particular utility. Theprocess module design can be employed for CVD of a number of differenttypes of layers, including epitaxial deposition of silicon on a singlesubstrate at a time.

[0025] A plurality of heat sources are supported outside the processchamber 30, to provide heat energy to the process chamber 30 and itscontents without appreciable absorption by the quartz chamber 30 walls.While the preferred embodiments are described in the context of a “coldwall” CVD reactor for processing semiconductor wafers, it will beunderstood that the processing methods described herein will haveutility in conjunction with other heating/cooling systems, such as thoseemploying inductive or resistive heating.

[0026] In the preferred embodiment, the plurality of heat sourcescomprises radiant heat lamps 20. In accordance with FIG. 1, the radiantheat lamps 20 are placed above and below the quartz process chamber 30,and are oriented parallel to the horizontal plane of the quartz processchamber 30. The above and below radiant heat lamps 20 are outside theprocess chamber 30, providing a radiant energy 22 in a direction towardsthe quartz process chamber 30 and its contents within.

[0027] A substrate, such as a silicon wafer 24, is shown supportedwithin the quartz process chamber 30 upon a wafer support or susceptor26. Note that while the substrate of the illustrated embodiment is asingle crystal silicon wafer, it will be understood that the term“substrate” broadly refers to any surface on which a layer is to bedeposited. The semiconductor wafer 24 and susceptor 26 within the quartzprocess chamber 30 are parallel to the horizontal plane of the quartzprocess chamber 30 and the radiant heat lamps 20.

[0028] A highly reflective surface 32 is preferably behind the radiantheat lamps, possibly surrounding above and below the quartz processchamber 30 and its contents therein. The highly reflective surface 32promotes a more efficient conveyance of radiant energy from the radiantheat lamps 20 to the wafer 24 as symbolized by the lines 22 in FIG. 1.Moreover, radiant energy 22 emitted from within the quartz processchamber 30 may also reflect against the highly reflective surface 32back towards the quartz process chamber 30 and its contents as indicatedby radiation lines in both directions, in FIG. 2.

[0029] In FIGS. 1 and 2, moveable radiation-absorbing medium or materialelements 34 are shown outside of the process module 10. In FIG. 3, themoveable material elements 34 are positioned inside the process module10, aligned parallel to the horizontal plane of the quartz processchamber 30 and the radiant heat lamps 20, and positioned between thechamber and the lamps.

[0030] While the element 34 in FIG. 3 is outside the chamber 30, one ofordinary skill in the art will recognize the utility of the element 34in other locations, including within the chamber 30. In an alternateembodiment, an absorption material element 34 may be introduced withinthe process chamber 30, but far enough away from the wafer 24 tominimize particle contamination of the wafer. Spacing between thematerial element 34 and the wafer 24 is preferably greater than about 2mm, more preferably greater than about 5 mm and most preferably greaterthan about 1 cm.

[0031] In another alternate embodiment, the process chamber comprises adouble-wall quartz chamber 44. In accordance with FIG. 4, thedouble-wall quartz chamber 44 comprises an inlet 38 and an outlet 40,through which a radiation absorption medium may flow. A radiationabsorption medium such or as water 36 may flow in through inlet 38 andout through outlet 40 in a sheet-like formation as illustrated in FIG.5. The laminar flow of the water 36 in a sheet-like formation is flushedbetween the walls of the double-wall quartz chamber 44 to coverpreferably more than about 85%, more preferably more than about 90%, andmost preferably more than about 95% of the surface area of eachdouble-wall.

[0032] Semiconductor Process

[0033] As indicated in the flow chart of FIG. 6, a first step 100 in thepreferred method is to load a substrate or semiconductor wafer 24 intothe quartz process chamber 30 (FIG. 1). A load arm (not shown) insertsthe semiconductor wafer into the quartz process chamber 30 and places iton the wafer support or susceptor 26. Once the semiconductor wafer 24 issecured on the susceptor 26, the robot arm retracts from the quartzprocess chamber, allowing for a semiconductor process to begin.

[0034] Referring again to the flow chart of FIG. 6, after asemiconductor wafer is loaded in the preferred quartz-processing chamber30, a semiconductor process begins, which may include heating 102 asubstrate. According to the illustrated embodiment of FIG. 1, theutilization of a radiant heat lamp 20 is the preferred method for theconveyance of a radiant energy 22 to a semiconductor wafer 24. Theradiant heat lamps 20 may be turned on or raised to a desired elevatedtemperature for the desired semiconductor process to commence. Also,with the highly reflective surfaces 32, a more efficient conveyance ofradiant energy 22 from the radiant heat lamps 20 to the semiconductorwafer 24 is promoted. Radiant energy 22 from the radiant heat lamps 20reflect against the highly reflective surfaces 32 and bounce backtowards the semiconductor wafer 24.

[0035] The next step in the preferred method illustrated in FIG. 6, isthe treatment 104 of the semiconductor wafer. The desired elevatedtemperature may vary depending on the type of treatment 104 that thesemiconductor wafer 24 will undergo. One particular wafer treatment is aCVD process called epitaxial deposition. Epitaxial deposition varies indeposition temperatures depending on the chemical sources used forsilicon epitaxy. For example, when it is desirable to use silicontetrachloride (SiCl₄) as a silicon source, the desired depositiontemperature would range from about 1150-1250° C. Using SiCi₄ at thattemperature range is advantageous in that very little deposition occurson process chamber walls, thereby reducing the frequency of cleaning.This in turn also results in lower particulate contamination, sincesilicon flaking off the inside walls of the process chambers walls isminimized. There is, however, significant autodoping and outdiffusion atsuch high process temperatures, which is generally undesirable in themanufacturing of sensitive semiconductor devices.

[0036] Conversely, however, temperatures can range as low as 950-1050°C. when using silicon sources like silane (SiH₄). These lowertemperatures ranges result in substantially less autodoping andoutdiffusion when compared to films deposited at higher temperatures.The most important disadvantage of using SiH₄ at these temperatures,however, is that it can decompose at low temperatures, causing heavydeposits on process chamber walls. This, in turn, would necessitate infrequent cleaning of the process chamber, reducing its effectivethroughput. Other treatments include processes like etching, annealingand diffusion—all of which may vary in process temperature ranges.

[0037] Cooling Method

[0038] Most treatment processes commonly share the subsequent need tocool the wafer before it proceeds to its next process which may be aphysical process, a chemical process, or a wafer transport process.After a wafer heating 104 process is completed, the wafer 24 isgenerally allowed to cool somewhat before the robot arm (not shown)retrieves the wafer 24 and delivers it to its next destination.Otherwise, the high temperature of the semiconductor wafer postprocessing may damage heat sensitive materials, such as plasticcassettes in which processed wafers are stored. Also, the robot arm maynot be able to tolerate handling heated substrates at high processtemperatures. Robot arms that can tolerate high process temperatures mayalso be too expensive. To cool the wafer after processing, the heatsources are turned down or off until the wafer is at least cool enoughfor the robot arm or wafer handler. Furthermore, in addition to simplycooling the semiconductor wafer to a safe temperature for transport andstorage, cooling should be fast enough not to impede wafer throughput.For example, wafer throughput may be compromised by the radiant energy22 emitted by the heated wafer 24. As illustrated in FIG. 2, the radiantenergy 22 may emit from the processed wafer towards the highlyreflective surfaces 32, and reflect back towards the processed wafer. Asa result, the processed wafer 24 may exhibit a slow and impeded cooling.

[0039] The high wafer throughput requirement is satisfied in accordancewith the illustrated embodiment of FIG. 3. Referring again to FIG. 6,the next step in the preferred method is to cool a semiconductor wafer24 by the introduction 106 of a radiation-absorbing medium or materialelement 34. The ability of a surface to emit or absorb by radiation isknown by the term emissivity. A perfect black body is an ideal body,which completely emits or absorbs radiant energy, and is defined ashaving an emissivity of 1.00, while all other surfaces have a loweremissivity expressed as a decimal value less than 1.00. Examples ofmediums suitable for the material element 34 include solids, liquids andgasses, particularly those that have high emissivities in the infraredradiation. Water, for example, with an emissivity value ranging from0.95-0.963, efficiently absorbs infrared radiation. The material element34 is preferably selected to absorb the wavelength of light radiated bythe heated wafer 24. This absorption feature advantageously enhances thecooling of energy emitting bodies such as the processed wafer 24 andsupport susceptor 26.

[0040] The moveable material element 34 is preferably utilized to coolthe semiconductor wafer expeditiously to a safe-handling temperature.The utilization of a radiation-absorbing medium or material element 34that efficiently absorbs infrared radiation after high temperatureprocessing, specifically infrared radiation in the range of 10 m, is thepreferred method for rapid cooling of the processed wafer 24. Theintroduction of the material element 34 after the semiconductorprocessing will not inhibit the conveyance of radiant energy duringprocess and will expedite the cooling of the wafer 24 and itssurrounding components like susceptor 26. According to the illustratedembodiment of FIG. 3, a radiation-absorbing material element 34 ispositioned on the either side of the quartz process chamber 30 and isparallel with wafer 24. When cooling of the energy emitting bodieswithin the process chamber 30 is needed, the radiation heat lamps 20will be turned off or lowered, and the radiation absorbing materialelement 34 is moved to a position in between the radiant heat lamps 20and the process chamber 30. Radiant energy 22 will be transferred fromthe energy emitting bodies, including the heated processed wafer 24 andsupport susceptor 26, to the material element 34, thus resulting intheir expedited cooling.

[0041] In accordance with another illustrated embodiment, FIG. 4illustrates the utilization of water 36 as a means to absorb radiation.By means of a double-wall quartz chamber 44, water can be flushed withinthe walls of the double-wall quartz process chamber 44, acting as a highabsorption material. Water is an efficient radiation absorptionmaterial, especially radiation in the infrared range. The double-wallquartz chamber 44 is preferably without water during the processduration of the wafer 24, allowing for an efficient conveyance ofradiant energy 22 from the radiant heat lamps 20 to the wafer. After theprocess is completed, cooling of the processed wafer 24 is morepreferably expedited by continuously flushing water 36 between thedouble-wall quartz chamber 44. The water 36 is conducted in through aninlet 38 and out through an outlet 40 of the double-wall quartz chamber44. Referring to FIG. 5, water 36 preferably flushes through inlet 38and spreads out in a sheet-like formation within the double-wall quartzchamber 44. The laminar flow of water 36 in a sheet-like formation isflushed between the walls of the double-wall quartz chamber 44 to coverpreferably more than about 85%, more preferably more than about 90%, andmost preferably more than about 95% of the surface area of eachdouble-wall. The sheet like formation of the water 36 within thedouble-wall quartz chamber 44 advantageously allows for a greaterabsorption surface area. The laminar flow of water in a sheet-likeformation absorbs radiant energy 22 from energy emitting bodies such aswafer 24 and susceptor 26, until the desired lowered temperature of theprocessed wafer 24 is reached expeditiously.

[0042] Referring again to the flow chart of FIG. 6, the next step in thepreferred method is to unload 108 the processed wafer 24. Aftertreatment 104 and subsequent cooling 106 of the semiconductor wafer, theload arm (not shown) may retrieve the processed wafer 24 for safetransport to its next destination, including the wafer handler (notshown) and/or wafer cassettes (not shown).

[0043] Once unloaded, the quartz process chamber 30 may be ready to loadthe next wafer 24 to be treated 102. Incidentally, for the next wafer 24to be expeditiously ramped to its preferred process temperature range,FIG. 2 illustrates how the radiation-absorbing material element 34 maybe returned to a location outside the process module. The materialelement 34 outside the process module allows for an efficient conveyanceof radiant energy 22 from the radiant heat lamps 20 to the wafer 24 tobe processed. Similarly, the water 36 between the double-wall processchamber 44 can then be emptied out for the next semiconductor wafer 24to be processed.

[0044] Alternatively, absorption of radiated energy 22 from energyemitting bodies, such as the wafer 24 and susceptor 26 can also occur byintroducing an absorption material element 34 within the processchamber. After a semiconductor process has taken place, and subsequentcooling is required, an absorption material medium 34 may be introducedwithin the process chamber 30, but far enough away from the wafer 24 tominimize particle contamination of wafer. Cooling by close proximitymaterial placement, or conduction, is preferably avoided to minimizecontamination opportunities.

[0045] Accordingly, several objects and advantages are inherent to thedescribed invention. For example, radiation cooling by the utilizationof a radiation absorbing material element is highly efficient andeffective, particularly for systems or processes that are heated byradiation. Similarly, the use of the radiation absorbing materialelement will result in very fast cooling of the system or process, justas efficiently and effectively as rapid heating by radiation in the samesystem or process. The use of radiation absorbing material medium canalso shorten process time and increase yield or throughput when coolingis involved in the process. Furthermore, the use of radiation absorbingmaterial element can be more cost effective than other cooling methods,for example, increasing gas flows inside the system or process chamber.The use of radiation absorbing material medium can also enable acontrolled cooling, if needed, by tuning the emissivity or radiationabsorbing efficiency of the absorption medium; and the use of radiationabsorbing material medium outside the process chamber will not causecontamination or particles to the systems or processes.

We claim:
 1. A method of processing workpieces, comprising: placing aworkpiece on a support within a process chamber; processing theworkpiece at an elevated temperature; moving a radiation absorbingmedium to a position between a reflective surface and the wafer afterprocessing the workpiece, the medium being spaced from the workpiecegreater than about 5 mm; and allowing the workpiece to cool from theelevated temperature.
 2. The method of claim 1 , wherein the radiationabsorbing medium is between a heat source and workpiece in the position.3. The method of claim 1 wherein the medium is solid, liquid or gashaving high emissivity, particularly in the infrared range
 4. A methodof processing a semiconductor substrate, comprising: placing a substrateon a substrate support within a semiconductor process chamber; heatingthe substrate to a processing temperature; and moving a radiationabsorbing medium to a position between a reflective surface and thesubstrate after heating the substrate, the position located outside theprocessing chamber.
 5. The method of claim 4 , wherein the radiationabsorbing medium is between the radiant heat source and the substrate atthe position.
 6. The method of claim 4 , further comprising removing themedium from the position prior to processing a subsequent substrate. 7.A high temperature processing apparatus, comprising: a processingchamber in which a substrate is placed for processing; a substratesupport within the processing chamber for supporting the substrate; aheat source positioned outside the processing chamber to provide radiantenergy to the substrate; a reflective surface of a high reflectivitycoating displaced outside the heat source, enhancing the energyconveyance to the substrate; and a movable radiation-absorbing materialelement, wherein the apparatus is configured to move the movable elementfrom a process position that does not interfere with heating thesubstrate during a fabrication process to a post-process positionbetween the reflective surface and the substrate after the fabricationprocess.
 8. The apparatus of claim 7 wherein the heat source comprises aplurality of radiant heat sources, disposed above and below thesubstrate.
 9. The apparatus of claim 7 further comprising a plurality ofreflective surfaces, disposed above and below the substrate.
 10. Theapparatus of claim 7 further comprising a radiation-absorbing mediumpositioned between the heat source and the substrate.
 11. The apparatusof claim 7 wherein the chamber comprises a double-wall quartz chamberwith a space between the double-walls.
 12. The apparatus of claim 11wherein the movable element comprises a movable radiation absorptionmedium between the double-wall.
 13. The apparatus of claim 12 whereinthe medium is water.
 14. The apparatus of claim 7 , wherein the processposition is located outside the processing chamber.
 15. The apparatus ofclaim 8 , wherein the post-process position is located outside theprocessing chamber.
 16. The apparatus of claim 7 , wherein the mediumspeeds cooling of the substrate when in the post-process position.